1. Field of the Invention
The present invention relates to an optical detecting apparatus (optical encoder) and a coordinate inputting apparatus using the detecting apparatus.
2. Description of the Related Art
Coordinate inputting apparatuses, e.g., a mouse and a trackball used to input position coordinate data indicating the position of a cursor or the like on a display screen of a personal computer or the like, are known. Such apparatuses have a ball and are capable of changing the displayed position of a cursor according to the direction and amount of rotation of the ball.
FIG. 4 is a diagram showing the construction of a mechanism of such a coordinate inputting apparatus.
A ball 1 shown in FIG. 4 is supported so as to be rotatable about its center point. Rollers 3X and 3Y fixed to rotatable shafts 2X and 2Y are pressed against the surface of the ball 1 at two points in radial directions form the center point of the ball 1 at an angle of 90.degree. from each other. The direction of arrow X in FIG. 4 will be referred to as "+X direction" in the XY coordinate system (the opposite direction referred to as "-X direction") and the direction of arrow Y will be referred to as "+Y direction" in the XY coordinate system (the opposite direction referred to as "-Y direction"). Disk-like choppers 4X and 4Y are respectively fixed to end portions of the shafts 2X and 2Y. A plurality of slits uniform in size are formed in an outer portion of each of the choppers 4X and 4Y along the entire circumferential length thereof.
A photointerrupter 5X is provided in association with the chopper 4X while a photointerrupter 5Y is provided in association with the chopper 4Y. Each of the photointerrupters 5X and 5Y has light emitting elements (not shown) and light receiving elements (not shown). The photointerrupters 5X and 5Y are disposed so that the outer portion of each chopper is interposed between the light emitting elements and the light receiving elements. The chopper 4X and the photointerrupter 5X form an optical encoder unit 6X while the chopper 4Y and the photointerrupter 5Y form an optical encoder unit 6Y.
In this arrangement, when the ball 1 rotates, the shafts 2X and 2Y are rotated by the rollers 3X and 3Y, and the choppers 4X and 4Y are also rotated thereby. On the other hand, a power supply voltage V is applied to the photointerrupters 5X and 5Y to cause the light emitting elements to constantly emit light. Therefore, as the choppers 4X and 4Y rotate, blade portions between the slits formed in the outer portion of each chopper successively passes the place between the light emitting elements and the light receiving elements of the corresponding photointerrupter 5X or 5Y. Light traveling from the light emitting elements to the light receiving elements is thereby chopped so that the levels of output signals XA and XB or YA and YB change in a pulsating manner.
FIG. 5 is a circuit diagram showing the configuration of an example of the optical encoder unit of the above-described coordinate inputting apparatus.
In this example, the light emitting elements of the photointerrupter 5A are light emitting diodes LED while the light receiving elements of the photointerrupter 5A are phototransistors Ph-Tr.
According to the rotation of the chopper 4X or 4Y, output light from each of the light emitting diodes LED is allowed to travel to the corresponding phototransistor Ph-Tr or stopped. When output light from the light emitting diode LED reaches the phototransistor Ph-Tr, the phototransistor Ph-Tr is turned on. When the phototransistor Ph-Tr is turned on, a signal of a predetermined potential is input to a Schmitt trigger gate 42 via the phototransistor Ph-Tr. The Schmitt trigger gate 42 removes noise from the input signal and outputs the signal.
Of the outputs signals XA, XB, YA, and YB generated in this manner, output signals XA and XB are used for detecting an X-axis component of the rotation of the ball 1 while output signals YA and YB are used for detecting a Y-axis component of the rotation of the ball 1.
Output signals XA and XB change in phase relation between rises of their pulses according to the direction of rotation of the chopper 4X (i.e., the direction of rotation of the ball 1). That is, when the ball 1 rotates in the +X direction, output signal XA rises earlier than output signal XB. When the ball 1 rotates in the -X direction, output signal XB rises earlier than output signal XA. The direction of rotation of the chopper 4X can be detected from the phase relationship between output signals XA and XB.
Output signals YA and YB also have a similar phase relationship.
The phototransistors shown in FIG. 5 have different light receiving sensitivities (that is, vary in light receiving sensitivity). Therefore, there is a need to correct variations in the receiving sensitivities of the phototransistors by adjusting the resistance values of resistors RXA, RAB, RYA, and RYB at the time of assembly of the apparatus.
Also, in the circuit shown in FIG. 5, the operating voltage range is considerably restricted (or fixed).
FIG. 6 shows the configuration of another conventional optical encoder unit designed to solve these problems. Output signals XA, XB, YA, and YB shown in FIG. 6 correspond to those in the circuit shown in FIG. 5.
In the circuit shown in FIG. 6, each of phototransistors Ph-Tr is turned on and off according to the rotation of chopper 4X or 4Y to change its emitter potential, as is the corresponding transistor in the circuit shown in FIG. 5.
Each of comparators 51 compares the emitter potential of one of the phototransistors Ph-Tr with a predetermined reference potential and outputs the comparison result as output signal XA, XB, YA, or YB.
Each of capacitors C is charged by emitter currents form the phototransistors to produce and hold the reference potential when the power supply is turned on.
In the circuit shown in FIG. 6, both the two potentials compared by one comparator 51 are produced from a common potential (emitter potential of phototransistor Ph-Tr). Therefore, a variation in the light receiving sensitivity of the corresponding phototransistor Ph-Tr equally influences the two potentials compared by the comparator 51. Accordingly, such a variation is canceled out at the time of comparison of the two potentials. In the circuit shown in FIG. 6, therefore, there is no need for correction of variations in the light receiving sensitivities of the phototransistors Ph-Tr.
Also in the circuit shown in FIG. 6, both the two potentials compared by one comparator 51 are produced from the common power supply line connected to the corresponding pohototransistor Ph-Tr. Therefore, a variation in the power supply voltage equally influences the two potentials compared by the comparator 51. Accordingly, such a variation is canceled out at the time of comparison of the two potentials. In the circuit shown in FIG. 6, therefore, the operating voltage range of the power supply can be increased.
The circuit shown in FIG. 6, however, requires charging of the capacitors C after a moment at which the power supply is turned on. There is, therefore, a problem of a long time (about five seconds, for example) being taken to stabilize the operation after turning on the power supply.
Further, if, in the circuits shown in FIGS. 5 and 6, the power supply is off when the mouse is stopped, and if the power supply is turned on after the movement of the mouse has been started, then the mouse operation cannot be followed up to detect the distance by which the mouse is moved. In these circuits, therefore, the light emitting diodes LED must always be maintained in the light emitting state to monitor the rotation of each of choppers 4X and 4Y even when the mouse is stopped. This is an obstacle to saving the power consumed by the light emitting diodes. The power consumption by light emitting elements has been a serious consideration with respect to battery drive, in particular.